mirror metadata refs after EnsureMetadataBranch writes

EnsureMetadataBranch advances the v1 branch from origin or creates a fresh orphan during setup, but the new committed-ref mirror was only updated by later hook-time writes. In v1.1 mode the mirror stayed unset between entire enable and the first session-end condensation, so every NewCommittedReadStore consumer (list/status/dispatch/rewind/ review) returned empty.

Mirror after each SetReference that advances the v1 branch, and thread ctx through the function so the mirror, the pre-existing Debug log, and SignCommitBestEffort share the caller's context.